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  • richardmitnick 10:14 am on March 18, 2019 Permalink | Reply
    Tags: "Exotic “second sound” phenomenon observed in pencil lead", , , , MIT, , There’s good reason to believe that second sound might be more pronounced in graphene even at room temperature., Transient thermal grating   

    From MIT News: “Exotic “second sound” phenomenon observed in pencil lead” 

    MIT News
    MIT Widget

    From MIT News

    March 14, 2019
    Jennifer Chu

    1
    Researchers find evidence that heat moves through graphite similar to the way sound moves through air. Image: Christine Daniloff

    At relatively balmy temperatures, heat behaves like sound when moving through graphite, study reports.

    The next time you set a kettle to boil, consider this scenario: After turning the burner off, instead of staying hot and slowly warming the surrounding kitchen and stove, the kettle quickly cools to room temperature and its heat hurtles away in the form of a boiling-hot wave.

    We know heat doesn’t behave this way in our day-to-day surroundings. But now MIT researchers have observed this seemingly implausible mode of heat transport, known as “second sound,” in a rather commonplace material: graphite — the stuff of pencil lead.

    At temperatures of 120 kelvin, or -240 degrees Fahrenheit, they saw clear signs that heat can travel through graphite in a wavelike motion. Points that were originally warm are left instantly cold, as the heat moves across the material at close to the speed of sound. The behavior resembles the wavelike way in which sound travels through air, so scientists have dubbed this exotic mode of heat transport “second sound.”

    The new results represent the highest temperature at which scientists have observed second sound. What’s more, graphite is a commercially available material, in contrast to more pure, hard-to-control materials that have exhibited second sound at 20 K, (-420 F) — temperatures that would be far too cold to run any practical applications.

    The discovery, published today in Science, suggests that graphite, and perhaps its high-performance relative, graphene, may efficiently remove heat in microelectronic devices in a way that was previously unrecognized.

    “There’s a huge push to make things smaller and denser for devices like our computers and electronics, and thermal management becomes more difficult at these scales,” says Keith Nelson, the Haslam and Dewey Professor of Chemistry at MIT. “There’s good reason to believe that second sound might be more pronounced in graphene, even at room temperature. If it turns out graphene can efficiently remove heat as waves, that would certainly be wonderful.”

    The result came out of a long-running interdisciplinary collaboration between Nelson’s research group and that of Gang Chen, the Carl Richard Soderberg Professor of Mechanical Engineering and Power Engineering. MIT co-authors on the paper are lead authors Sam Huberman and Ryan Duncan, Ke Chen, Bai Song, Vazrik Chiloyan, Zhiwei Ding, and Alexei Maznev.

    “In the express lane”

    Normally, heat travels through crystals in a diffusive manner, carried by “phonons,” or packets of acoustic vibrational energy. The microscopic structure of any crystalline solid is a lattice of atoms that vibrate as heat moves through the material. These lattice vibrations, the phonons, ultimately carry heat away, diffusing it from its source, though that source remains the warmest region, much like a kettle gradually cooling on a stove.

    The kettle remains the warmest spot because as heat is carried away by molecules in the air, these molecules are constantly scattered in every direction, including back toward the kettle. This “back-scattering” occurs for phonons as well, keeping the original heated region of a solid the warmest spot even as heat diffuses away.

    However, in materials that exhibit second sound, this back-scattering is heavily suppressed. Phonons instead conserve momentum and hurtle away en masse, and the heat stored in the phonons is carried as a wave. Thus, the point that was originally heated is almost instantly cooled, at close to the speed of sound.

    Previous theoretical work in Chen’s group had suggested that, within a range of temperatures, phonons in graphene may interact predominately in a momentum-conserving fashion, indicating that graphene may exhibit second sound. Last year, Huberman, a member of Chen’s lab, was curious whether this might be true for more commonplace materials like graphite.

    Building upon tools previously developed in Chen’s group for graphene, he developed an intricate model to numerically simulate the transport of phonons in a sample of graphite. For each phonon, he kept track of every possible scattering event that could take place with every other phonon, based upon their direction and energy. He ran the simulations over a range of temperatures, from 50 K to room temperature, and found that heat might flow in a manner similar to second sound at temperatures between 80 and 120 K.

    Huberman had been collaborating with Duncan, in Nelson’s group, on another project. When he shared his predictions with Duncan, the experimentalist decided to put Huberman’s calculations to the test.

    “This was an amazing collaboration,” Chen says. “Ryan basically dropped everything to do this experiment, in a very short time.”

    “We were really in the express lane with this,” Duncan adds.

    Upending the norm

    Duncan’s experiment centered around a small, 10-square-millimeter sample of commercially available graphite.

    Using a technique called transient thermal grating, he crossed two laser beams so that the interference of their light generated a “ripple” pattern on the surface of a small sample of graphite. The regions of the sample underlying the ripple’s crests were heated, while those that corresponded to the ripple’s troughs remained unheated. The distance between crests was about 10 microns.

    Duncan then shone onto the sample a third laser beam, whose light was diffracted by the ripple, and its signal was measured by a photodetector. This signal was proportional to the height of the ripple pattern, which depended on how much hotter the crests were than the troughs. In this way, Duncan could track how heat flowed across the sample over time.

    If heat were to flow normally in the sample, Duncan would have seen the surface ripples slowly diminish as heat moved from crests to troughs, washing the ripple pattern away. Instead, he observed “a totally different behavior” at 120 K.

    Rather than seeing the crests gradually decay to the same level as the troughs as they cooled, the crests actually became cooler than the troughs, so that the ripple pattern was inverted — meaning that for some of the time, heat actually flowed from cooler regions into warmer regions.

    “That’s completely contrary to our everyday experience, and to thermal transport in almost every material at any temperature,” Duncan says. “This really looked like second sound. When I saw this I had to sit down for five minutes, and I said to myself, ‘This cannot be real.’ But I ran the experiment overnight to see if it happened again, and it proved to be very reproducible.”

    According to Huberman’s predictions, graphite’s two-dimensional relative, graphene, may also exhibit properties of second sound at even higher temperatures approaching or exceeding room temperature. If this is the case, which they plan to test, then graphene may be a practical option for cooling ever-denser microelectronic devices.

    “This is one of a small number of career highlights that I would look to, where results really upend the way you normally think about something,” Nelson says. “It’s made more exciting by the fact that, depending on where it goes from here, there could be interesting applications in the future. There’s no question from a fundamental point of view, it’s really unusual and exciting.”

    This research was funded in part by the Office of Naval Research, the Department of Energy, and the National Science Foundation.

    See the full article here .


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  • richardmitnick 2:23 pm on March 15, 2019 Permalink | Reply
    Tags: A first step toward vector nanoscale magnetometry, Measuring atomic-scale magnetic fields with great precision, MIT, Nitrogen-vacancy centers in diamond, Research Laboratory of Electronics, Useful for testing biological samples without damaging them   

    From MIT News: “Quantum sensing method measures minuscule magnetic fields” 

    MIT News
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    From MIT News

    March 15, 2019
    David L. Chandler

    3
    Credit: CC0 Public Domain

    1
    The experimental setup used by the researchers to test their magnetic sensor system, using green laser light for confocal microscopy. Photos courtesy of Research Laboratory of Electronics

    2
    The experimental setup used by the researchers to test their sensor system. The sample being tested is on the stage just below the narrow end of the green box, right of center, which houses magnets. Photos courtesy of Research Laboratory of Electronics

    A new way of measuring atomic-scale magnetic fields with great precision, not only up and down but sideways as well, has been developed by researchers at MIT. The new tool could be useful in applications as diverse as mapping the electrical impulses inside a firing neuron, characterizing new magnetic materials, and probing exotic quantum physical phenomena.

    The new approach is described today in the journal Physical Review Letters in a paper by graduate student Yi-Xiang Liu, former graduate student Ashok Ajoy, and professor of nuclear science and engineering Paola Cappellaro.

    The technique builds on a platform already developed to probe magnetic fields with high precision, using tiny defects in diamond called nitrogen-vacancy (NV) centers. These defects consist of two adjacent places in the diamond’s orderly lattice of carbon atoms where carbon atoms are missing; one of them is replaced by a nitrogen atom, and the other is left empty. This leaves missing bonds in the structure, with electrons that are extremely sensitive to tiny variations in their environment, be they electrical, magnetic, or light-based.

    Previous uses of single NV centers to detect magnetic fields have been extremely precise but only capable of measuring those variations along a single dimension, aligned with the sensor axis. But for some applications, such as mapping out the connections between neurons by measuring the exact direction of each firing impulse, it would be useful to measure the sideways component of the magnetic field as well.

    Essentially, the new method solves that problem by using a secondary oscillator provided by the nitrogen atom’s nuclear spin. The sideways component of the field to be measured nudges the orientation of the secondary oscillator. By knocking it slightly off-axis, the sideways component induces a kind of wobble that appears as a periodic fluctuation of the field aligned with the sensor, thus turning that perpendicular component into a wave pattern superimposed on the primary, static magnetic field measurement. This can then be mathematically converted back to determine the magnitude of the sideways component.

    The method provides as much precision in this second dimension as in the first dimension, Liu explains, while still using a single sensor, thus retaining its nanoscale spatial resolution. In order to read out the results, the researchers use an optical confocal microscope that makes use of a special property of the NV centers: When exposed to green light, they emit a red glow, or fluorescence, whose intensity depends on their exact spin state. These NV centers can function as qubits, the quantum-computing equivalent of the bits used in ordinary computing.

    “We can tell the spin state from the fluorescence,” Liu explains. “If it’s dark,” producing less fluorescence, “that’s a ‘one’ state, and if it’s bright, that’s a ‘zero’ state,” she says. “If the fluorescence is some number in between then the spin state is somewhere in between ‘zero’ and ‘one.’”

    The needle of a simple magnetic compass tells the direction of a magnetic field, but not its strength. Some existing devices for measuring magnetic fields can do the opposite, measuring the field’s strength precisely along one direction, but they tell nothing about the overall orientation of that field. That directional information is what the new detector system can n provide.

    In this new kind of “compass,” Liu says, “we can tell where it’s pointing from the brightness of the fluorescence,” and the variations in that brightness. The primary field is indicated by the overall, steady brightness level, whereas the wobble introduced by knocking the magnetic field off-axis shows up as a regular, wave-like variation of that brightness, which can then be measured precisely.

    An interesting application for this technique would be to put the diamond NV centers in contact with a neuron, Liu says. When the cell fires its action potential to trigger another cell, the system should be able to detect not only the intensity of its signal, but also its direction, thus helping to map out the connections and see which cells are triggering which others. Similarly, in testing new magnetic materials that might be suitable for data storage or other applications, the new system should enable a detailed measurement of the magnitude and orientation of magnetic fields in the material.

    Unlike some other systems that require extremely low temperatures to operate, this new magnetic sensor system can work well at ordinary room temperature, Liu says, making it feasible to test biological samples without damaging them.

    The technology for this new approach is already available. “You can do it now, but you need to first take some time to calibrate the system,” Liu says.

    For now, the system only provides a measurement of the total perpendicular component of the magnetic field, not its exact orientation. “Now, we only extract the total transverse component; we can’t pinpoint the direction,” Liu says. But adding that third dimensional component could be done by introducing an added, static magnetic field as a reference point. “As long as we can calibrate that reference field,” she says, it would be possible to get the full three-dimensional information about the field’s orientation, and “there are many ways to do that.”

    Amit Finkler, a senior scientist in chemical physics at Israel’s Weizmann Institute, who was not involved in this work, says “This is high quality research. … They obtain a sensitivity to transverse magnetic fields on par with the DC sensitivity for parallel fields, which is impressive and encouraging for practical applications.”

    Finkler adds, “As the authors humbly write in the manuscript, this is indeed the first step toward vector nanoscale magnetometry. It remains to be seen whether their technique can indeed be applied to actual samples, such as molecules or condensed matter systems.” However, he says, “The bottom line is that as a potential user/implementer of this technique, I am highly impressed and moreover encouraged to adopt and apply this scheme in my experimental setups.”

    While this research was specifically aimed at measuring magnetic fields, the researchers say the same basic methodology could be used to measure other properties of molecules including rotation, pressure, electric fields, and other characteristics. The research was supported by the National Science Foundation and the U.S. Army Research Office.

    See the full article here .


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  • richardmitnick 5:40 pm on March 4, 2019 Permalink | Reply
    Tags: "Technique streamlines fabrication of 2-D circuits", by growing a 2-D material directly onto a patterned substrate and recycling the circuit patterns, Due to the weak interaction between MoS2 and the growth substrate the researchers found they could detach the MoS2 cleanly from the original substrate by submerging it in water, In their study the researchers recycled the same patterned substrate four times without seeing signs of wear, MIT, onto a growth substrate in a chosen pattern, Researchers from MIT and elsewhere describe a technique that streamlines the fabrication process, The researchers carefully grow a single layer of molybdenum disulfide (MoS2), The researchers used traditional photolithography masks on a silicon oxide substrate, To design a pattern on a growth substrate the researchers leveraged a technique that uses oxygen-based plasma to carve patterns into a substrate’s surface, which is just three atoms thick, With the new method using only water the researchers can transfer the material from its growth substrate to its destination substrate so cleanly that the original patterned substrate can be reused as   

    From MIT News: “Technique streamlines fabrication of 2-D circuits” 

    MIT News
    MIT Widget

    From MIT News

    March 4, 2019
    Rob Matheson

    1
    MIT researchers have developed a technique to grow 2-D materials directly onto patterned substrates (shown here) and then recycle the patterns for faster, simpler chip manufacturing.
    Courtesy of the researchers.

    Growing material directly onto substrates and recycling chip patterns should enable faster, simpler manufacturing.

    Exotic 2-D materials hold great promise for creating atom-thin circuits that could power flexible electronics, optoelectronics, and other next-generation devices. But fabricating complex 2-D circuits requires multiple time-consuming, expensive steps.

    In a paper published in PNAS, researchers from MIT and elsewhere describe a technique that streamlines the fabrication process, by growing a 2-D material directly onto a patterned substrate and recycling the circuit patterns.

    The researchers carefully grow a single layer of molybdenum disulfide (MoS2), which is just three atoms thick, onto a growth substrate in a chosen pattern. This approach differs from traditional techniques that grow and etch away a material iteratively, over multiple layers. Those processes take a while and increase the chances of causing surface defects that may hinder the performance of the material.

    With the new method, using only water, the researchers can transfer the material from its growth substrate to its destination substrate so cleanly that the original patterned substrate can be reused as a “master-replica” type of mold — meaning a reusable template for manufacturing. In traditional fabrication, growth substrates get tossed after each material transfer, and the circuit must be patterned again on a new substrate to regrow more material.

    “When we scale up and make more complex electronic devices, people need to integrate numerous 2-D materials into more layers and specific shapes. If we follow traditional methods, step by step, it will be very time consuming and inefficient,” says the first author Yunfan Guo, a postdoc in the Department of Electrical Engineering and Computer Science (EECS) and the Research Laboratory of Electronics. “Our method shows the potential to make the whole fabrication process simpler, lower cost, and more efficient.”

    In their work, the researchers fabricated arbitrary patterns and a working transistor made from MoS2, which is one of the thinnest known semiconductors. In their study, the researchers recycled the same patterned substrate four times without seeing signs of wear.

    Guo is joined on the paper by EECS professors Tomas Palacios and Jing Kong; Ju Li, an MIT professor of nuclear science and engineering; Xi Ling of Boston University; Letian Dou and Enzheng Shi of Purdue University; seven other MIT graduate students, postdocs, and alumni; and two other co-authors from Cornell University and Purdue University.

    Controlled growth

    To design a pattern on a growth substrate, the researchers leveraged a technique that uses oxygen-based plasma to carve patterns into a substrate’s surface. Some version of this technique has been used experimentally before to grow 2-D material patterns. But the spatial resolution — meaning the size of precise structures that can be fabricated — is relatively poor (100 microns), and the electrical performance has been much lower than materials grown using other methods.

    To fix this, the researchers conducted in-depth studies into how MoS2 atoms arrange themselves on a substrate surface and how certain chemical precursors can help control the material’s growth. In doing so, they were able to leverage the technique to grow a single layer of high-quality MoS2 within precise patterns.

    The researchers used traditional photolithography masks on a silicon oxide substrate, where the desired pattern lies within regions unexposed to light. Those regions are subsequently exposed to the oxygen-based plasma. The plasma etches away about 1-2 nanometers of the substrate in the pattern.

    This process also creates a higher surface energy and an enhanced affinity for water-loving (“hydrophilic”) molecules in these plasma-treated regions. The researchers then use an organic salt, called PTAS, that acts as a growth promoter for MoS2. The salt is attracted to the newly created hydrophilic etched regions. In addition, the researchers used sulfur, an essential precursor for MoS2 growth, at a precise amount and temperature to regulate exactly how many of the material’s atoms will form on the substrate.

    When the researchers subsequently measured the MoS2 growth, they found it filled in about 0.7 nanometers of the etched pattern. That’s equivalent to exactly one layer of MoS2.

    Recycled patterns

    Next, the researchers developed a method to recycle the patterned substrate. Traditionally, transferring 2-D materials from a growth substrate onto a destination substrate, such as a flexible surface, requires encasing the whole grown material in a polymer, chemically etching it, and separating it from its growth substrate. But this inevitably brings in contaminants to the material. When the material released, it also leaves behind residue, so the original substrates may not be reused.

    Due to the weak interaction between MoS2 and the growth substrate, however, the researchers found they could detach the MoS2 cleanly from the original substrate by submerging it in water. This process, called “delamination,” eliminates the need for using any supporting layer and produces a clean break with the material from the substrate.

    “That’s why we can recycle it,” Guo says. “After it’s transferred, because it is purely clean, our patterned substrate is recovered and we can use it for multiple growths.”

    The researchers’ innovations introduce far fewer surface defects that limit performance, as measured in electron mobility — how fast electrons move through a semiconductor.

    In their paper, the researchers fabricated a 2-D transistor, called a field-effect transistor. Results indicate the electron mobility and “on-off ratio” — how efficiently a transistor flicks between the 1 and 0 computational states — are comparable with the reported values of traditionally grown high-quality, high-performance materials.

    The field-effect transistor currently has a spatial resolution of about 2 microns, which is limited only by the laser the microfabrication instruments the researchers used. Next, the researchers hope to shrink the pattern size, and directly integrate complex circuits on 2-D materials using their fabrication technique.

    See the full article here .


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    Please help promote STEM in your local schools.


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  • richardmitnick 12:49 pm on March 2, 2019 Permalink | Reply
    Tags: "Securing the 'internet of things' in the quantum age", A novel cryptography circuit that can be used to protect low-power “internet of things” (IoT) devices in the coming age of quantum computing, Bringing quantum computers online and to market could one day enable advances in medical research and drug discovery and other applications, But these schemes are way too computationally intense for IoT devices which can only spare enough energy for simple data processing, For their circuit design, Generating random numbers is the most important part of all cryptography schemes because those numbers are used to generate secure encryption keys that can’t be predicted, MIT, Next the researchers plan to tweak the chip to run all the lattice-based cryptography schemes listed in NIST’s second phase, NIST has been trying to find the most secure postquantum encryption schemes, On the hardware side the researchers made innovations in data flow, Quantum computers can in principle execute calculations that today are practically impossible for classical computers, The architecture is customizable to accommodate the multiple lattice-based schemes currently being studied in preparation for the day that quantum computers come online, The circuit also incorporates a small instruction memory component that can be programmed with custom instructions to handle different sampling techniques — such as specific probability distribution, The circuit is the first of its kind to meet standards for lattice-based cryptography set by the National Institute of Standards and Technology (NIST), The modified NTT splits vector data and allocates portions across four single-port RAM devices, the researchers modified a technique called “number theoretic transform” (NTT), Today’s most promising quantum-resistant encryption scheme is called “lattice-based cryptography” which hides information in extremely complicated mathematical structures. To date no known quant, which functions similarly to the Fourier transform mathematical technique that decomposes a signal into the multiple frequencies that make it up   

    From MIT News: “Securing the “internet of things” in the quantum age” 

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    MIT Widget

    From MIT News

    March 1, 2019
    Rob Matheson

    1
    MIT researchers have developed a novel chip that can compute complex quantum-proof encryption schemes efficiently enough to protect low-power “internet of things” (IoT) devices.
    Image courtesy of the researchers.

    Efficient chip enables low-power devices to run today’s toughest quantum encryption schemes.

    MIT researchers have developed a novel cryptography circuit that can be used to protect low-power “internet of things” (IoT) devices in the coming age of quantum computing.

    Quantum computers can in principle execute calculations that today are practically impossible for classical computers. Bringing quantum computers online and to market could one day enable advances in medical research, drug discovery, and other applications. But there’s a catch: If hackers also have access to quantum computers, they could potentially break through the powerful encryption schemes that currently protect data exchanged between devices.

    Today’s most promising quantum-resistant encryption scheme is called “lattice-based cryptography,” which hides information in extremely complicated mathematical structures. To date, no known quantum algorithm can break through its defenses. But these schemes are way too computationally intense for IoT devices, which can only spare enough energy for simple data processing.

    In a paper presented at the recent International Solid-State Circuits Conference, MIT researchers describe a novel circuit architecture and statistical optimization tricks that can be used to efficiently compute lattice-based cryptography. The 2-millimeter-squared chips the team developed are efficient enough for integration into any current IoT device.

    The architecture is customizable to accommodate the multiple lattice-based schemes currently being studied in preparation for the day that quantum computers come online. “That might be a few decades from now, but figuring out if these techniques are really secure takes a long time,” says first author Utsav Banerjee, a graduate student in electrical engineering and computer science. “It may seem early, but earlier is always better.”

    Moreover, the researchers say, the circuit is the first of its kind to meet standards for lattice-based cryptography set by the National Institute of Standards and Technology (NIST), an agency of the U.S. Department of Commerce that finds and writes regulations for today’s encryption schemes.

    Joining Banerjee on the paper are Anantha Chandrakasan, dean of MIT’s School of Engineering and the Vannevar Bush Professor of Electrical Engineering and Computer Science, and Abhishek Pathak of the Indian Institute of Technology.

    Efficient sampling

    In the mid-1990s, MIT Professor Peter Shor developed a quantum algorithm that can essentially break through all modern cryptography schemes. Since then, NIST has been trying to find the most secure postquantum encryption schemes. This happens in phases; each phase winnows down a list of the most secure and practical schemes. Two weeks ago, the agency entered its second phase for postquantum cryptography, with lattice-based schemes making up half of its list.

    In the new study, the researchers first implemented on commercial microprocessors several NIST lattice-based cryptography schemes from the agency’s first phase. This revealed two bottlenecks for efficiency and performance: generating random numbers and data storage.

    Generating random numbers is the most important part of all cryptography schemes, because those numbers are used to generate secure encryption keys that can’t be predicted. That’s calculated through a two-part process called “sampling.”

    Sampling first generates pseudorandom numbers from a known, finite set of values that have an equal probability of being selected. Then, a “postprocessing” step converts those pseudorandom numbers into a different probability distribution with a specified standard deviation — a limit for how much the values can vary from one another — that randomizes the numbers further. Basically, the random numbers must satisfy carefully chosen statistical parameters. This difficult mathematical problem consumes about 80 percent of all computation energy needed for lattice-based cryptography.

    After analyzing all available methods for sampling, the researchers found that one method, called SHA-3, can generate many pseudorandom numbers two or three times more efficiently than all others. They tweaked SHA-3 to handle lattice-based cryptography sampling. On top of this, they applied some mathematical tricks to make pseudorandom sampling, and the postprocessing conversion to new distributions, faster and more efficient.

    They run this technique using energy-efficient custom hardware that takes up only 9 percent of the surface area of their chip. In the end, this makes the process of sampling two orders of magnitude more efficient than traditional methods.

    Splitting the data

    On the hardware side, the researchers made innovations in data flow. Lattice-based cryptography processes data in vectors, which are tables of a few hundred or thousand numbers. Storing and moving those data requires physical memory components that take up around 80 percent of the hardware area of a circuit.

    Traditionally, the data are stored on a single two-or four-port random access memory (RAM) device. Multiport devices enable the high data throughput required for encryption schemes, but they take up a lot of space.

    For their circuit design, the researchers modified a technique called “number theoretic transform” (NTT), which functions similarly to the Fourier transform mathematical technique that decomposes a signal into the multiple frequencies that make it up. The modified NTT splits vector data and allocates portions across four single-port RAM devices. Each vector can still be accessed in its entirety for sampling as if it were stored on a single multiport device. The benefit is the four single-port REM devices occupy about a third less total area than one multiport device.

    “We basically modified how the vector is physically mapped in the memory and modified the data flow, so this new mapping can be incorporated into the sampling process. Using these architecture tricks, we reduced the energy consumption and occupied area, while maintaining the desired throughput,” Banerjee says.

    The circuit also incorporates a small instruction memory component that can be programmed with custom instructions to handle different sampling techniques — such as specific probability distributions and standard deviations — and different vector sizes and operations. This is especially helpful, as lattice-based cryptography schemes will most likely change slightly in the coming years and decades.

    Adjustable parameters can also be used to optimize efficiency and security. The more complex the computation, the lower the efficiency, and vice versa. In their paper, the researchers detail how to navigate these tradeoffs with their adjustable parameters. Next, the researchers plan to tweak the chip to run all the lattice-based cryptography schemes listed in NIST’s second phase.

    See the full article here .


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    Please help promote STEM in your local schools.


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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 3:52 pm on February 28, 2019 Permalink | Reply
    Tags: By tuning size illumination angle and curvature MIT engineers can produce brilliant colors in patterns they can predict in otherwise transparent droplets, MIT, Optical effect could be harnessed for light displays and litmus tests and makeup products,   

    From MIT News: “Engineers make clear droplets produce iridescent colors” 

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    From MIT News

    February 27, 2019
    Jennifer Chu

    1
    By tuning size, illumination angle, and curvature, MIT engineers can produce brilliant colors, in patterns they can predict, in otherwise transparent droplets. Image: Felice Frankel

    2
    Seen from above, transparent droplets in a Petri dish, illuminated with white light, appear as varying colors, depending on their size and shape. Courtesy of the researchers.

    Optical effect could be harnessed for light displays, litmus tests, and makeup products.

    Engineers at MIT and Penn State University have found that under the right conditions, ordinary clear water droplets on a transparent surface can produce brilliant colors, without the addition of inks or dyes.

    In a paper published today in Nature, the team reports that a surface covered in a fine mist of transparent droplets and lit with a single lamp should produce a bright color if each tiny droplet is precisely the same size.

    This iridescent effect is due to “structural color,” by which an object generates color simply due to the way light interacts with its geometric structure. The effect may explain certain iridescent phenomena, such as the colorful condensation on a plastic dish or inside a water bottle.

    The researchers have developed a model that predicts the color a droplet will produce, given specific structural and optical conditions. The model could be used as a design guide to produce, for example, droplet-based litmus tests, or color-changing powders and inks in makeup products.

    “Synthetic dyes used in consumer products to create bright colors might not be as healthy as they should be,” says Mathias Kolle, assistant professor of mechanical engineering at MIT. “As some of these dyes are more strongly regulated, companies are asking, can we use structural colors to replace potentially unhealthy dyes? Thanks to the careful observations by Amy Goodling and Lauren Zarzar at Penn State and to Sara’s modeling, which brought this effect and its physical explanation to light, there might be an answer.”

    Sara Nagelberg of MIT, along with lead author Goodling, Zarzar, and others from Penn State, are Kolle’s co-authors on the paper.

    Follow the rainbow

    Last year, Zarzar and Goodling were studying transparent droplet emulsions made from a mixture of oils of different density. They were observing the droplets’ interactions in a clear Petri dish, when they noticed the drops appeared surprisingly blue. They took a photo and sent it off to Kolle with a question: Why is there color here?

    Initially, Kolle thought the color might be due to the effect that causes rainbows, in which sunlight is redirected by rain drops and individual colors are separated into different directions. In physics, Mie scattering theory is used to describe the way spheres such as raindrops scatter a plane of electromagnetic waves, such as incoming sunlight. But the droplets that Zarzar and Goodling observed were not spheres, but rather, hemispheres or domes on a flat surface.

    “Initially we followed this rainbow-causing effect,” says Nagelberg, who headed up the modeling effort to try to explain the effect. “But it turned out to be something quite different.”

    She noted that the team’s hemispherical droplets broke symmetry, meaning they were not perfect spheres — a seemingly obvious fact but nevertheless an important one, as it meant that light should behave differently in hemispheres versus spheres. Specifically, the concave surface of a hemisphere allows an optical effect that is not possible in perfect spheres: total internal reflection, or TIR.

    Total internal reflection is a phenomenon in which light strikes an interface between a high refractive index medium (water, for instance) to a lower refractive index medium (such as air) at a high angle such that 100 percent of that light is reflected. This is the effect that allows optical fibers to carry light for kilometers with low loss. When light enters a single droplet, it is reflected by TIR along its concave interface.

    In fact, once light makes its way into a droplet, Nagelberg found that it can take different paths, bouncing two, three, or more times before exiting at another angle. The way light rays add up as they exit determines whether a droplet will produce color or not.

    For example, two rays of white light, containing all visible wavelengths of light, entering at the same angle and exiting at the same angle, could take entirely different paths within a droplet. If one ray bounces three times, it has a longer path than a ray that bounces twice, so that it lags behind slightly before exiting the droplet. If this phase lag results in the two rays’ waves being in phase (meaning the waves’ troughs and crests are aligned), the color corresponding to that wavelength will be visible. This interference effect, which ultimately produces color in otherwise clear droplets, is much stronger in small rather than large droplets.

    “When there is interference, it’s like kids making waves in a pool,” Kolle says. “If they do whatever they want, there’s no constructive adding up of effort, and just a lot of mess in the pool, or random wave patterns. But if they all push and pull together, you get a big wave. It’s the same here: If you get waves in phase coming out, you get more intensity of color.”

    A carpet of color

    The color that droplets produce also depends on structural conditions, such as the size and curvature of the droplets, along with the droplet’s refractive indices.

    Nagelberg incorporated all these parameters into a mathematical model to predict the colors that droplets would produce under certain structural and optical conditions. Zarzar and Goodling then tested the model’s predictions against actual droplets they produced in the lab.

    First, the team optimized their initial experiment, creating droplet emulsions, the sizes of which they could precisely control using a microfluidic device. They produced, as Kolle describes, a “carpet” of droplets of the exact same size, in a clear Petri dish, which they illuminated with a single, fixed white light. They then recorded the droplets with a camera that circled around the dish, and observed that the droplets exhibited brilliant colors that shifted as the camera circled around. This demonstrated how the angle at which light is seen to enter the droplet affects the droplet’s color.

    The team also produced droplets of various sizes on a single film and observed that from a single viewing direction, the color would shift redder as the droplet size increased, and then would loop back to blue and cycle through again. This makes sense according to the model, as larger droplets would give light more room to bounce, creating longer paths and larger phase lags.

    To demonstrate the importance of curvature in a droplet’s color, the team produced water condensation on a transparent film that was treated with a hydrophobic (water-repelling) solution, with the droplets forming the shape of an elephant. The hydrophobic parts created more concave droplets, whereas the rest of the film created shallower droplets. Light could more easily bounce around in the concave droplets, compared to the shallow droplets. The result was a very colorful elephant pattern against a black background.

    In addition to liquid droplets, the researchers 3-D-printed tiny, solid caps and domes from various transparent, polymer-based materials, and observed a similar colorful effect in these solid particles, that could be predicted by the team’s model.

    Kolle expects that the model may be used to design droplets and particles for an array of color-changing applications.

    “There’s a complex parameter space you can play with,” Kolle says. “You can tailor a droplet’s size, morphology, and observation conditions to create the color you want.”

    This research was supported, in part, by the National Science Foundation and the U. S. Army Research Office through the Institute for Soldier Nanotechnologies at MIT.

    See the full article here .


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  • richardmitnick 1:26 pm on February 26, 2019 Permalink | Reply
    Tags: "Plasma Science and Fusion Center leads new Center of Excellence", awrence Livermore National Laboratory-NIF, , General Atomics, MIT, , Sanda Lab Z machine,   

    From MIT News: “Plasma Science and Fusion Center leads new Center of Excellence” 

    MIT News
    MIT Widget

    From MIT News

    February 25, 2019
    Paul Rivenberg

    1
    Members of the the PSFC’s High-Energy-Density Physics division gather in their Accelerator Facility, part of the new Center of Excellence. Photo: Paul Rivenberg

    2
    Gathered around the conference table are (clockwise from front left) Research Scientist Maria Gatu Johnson, Senior Research Scientist Johan Frenje, Research Scientist Fredrick Seguin, Senior Research Scientist Chikang Li, and HEDP Division Head Richard Petrasso. Photo: Paul Rivenberg

    Award will support educational and research efforts in high-energy-density physics at MIT and four academic research partners.

    The High-Energy-Density Physics (HEDP) division of MIT’s Plasma Science and Fusion Center (PSFC), along with four other universities, has been awarded a five-year, $10 million grant to establish a Stewardship Science Academic Alliances Center of Excellence. The PSFC will be the lead partner in the center, which includes the University of Iowa; the University of Nevada at Reno; the University of Rochester; and Virginia Polytechnic Institute and State University.

    The U.S. Department of Energy’s (DOE) National Nuclear Security Administration (NNSA) award will support educational and research missions across the partners. The goal of the newly established center is to generate exceptional experimental and theoretical PhDs in HEDP and inertial confinement fusion (ICF), while addressing issues of critical interest to the Department of Energy’s NNSA and national labs.

    Officially called the Center for Advanced Nuclear Diagnostics and Platforms for Inertial ICF and HEDP at Omega, NIF and Z, the center will focus on the properties of plasma under extreme conditions of temperature, density and pressure. Center partners will collaborate closely with the Lawrence Livermore National Laboratory, Los Alamos National Laboratory, Sandia National Laboratory, the Laboratory for Laser Energetics, and General Atomics.

    U Rochester Laboratory for Laser Energetics

    1

    MIT’s HEDP division has a long and established history of collaboration with these labs, regularly using Laser Energetics’s 30-kilojoule OMEGA laser, Lawrence Livermore’s National Ignition Facility, and Sandia’s Z machine to pursue a wide range of research, including inertial confinement fusion, nuclear science, and laboratory astrophysics. The division has used its Accelerator Facility to develop and characterize diagnostics for these machines, and as part of the new center will pursue new diagnostic techniques for advanced research.

    U Rochester Omega Laser


    National Ignition Facility at LLNL

    Sandia Z machine

    HEDP division head and Center of Excellence Director Richard Petrasso acknowledges the importance of this partnership.

    “The center is about our work in inertial confinement fusion, and also in laboratory astrophysics, simulating aspects of astrophysical phenomena, such as the jetting in the crab nebula,” Petrasso says. “There is lots of interesting physics that students and staff have been observing for years. This new center allows us, with our partners, to really expand our investigations.”

    PSFC Director Dennis Whyte observed that the new center is a recognition of the HEDP division’s excellence. Thanking the team for the exceptional work, under the encouragement of the senior leadership, he said, “Your work is one of the gems of the PSFC. This division produces outstanding, unique science, and with a mission that is critical to national security.”

    Launched in 2002, the Stewardship Science Academic Alliances Centers of Excellence program emphasizes areas of research that are relevant to NNSA’s stockpile stewardship mission, and promotes the education of the next generation of highly-trained nuclear scientists and engineers.

    See the full article here .


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    Please help promote STEM in your local schools.


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  • richardmitnick 10:25 am on February 25, 2019 Permalink | Reply
    Tags: "Quantum dots can spit out clone-like photons", , , It’s a new phenomenon and will require much work to develop to a practical level, MIT, , Perovskite quantum dots still have a long way to go until they become applicable in real applications, , , , Such coherent photons could also be used for quantum-encrypted communications applications, The ability to produce individual photons with precisely known and persistent properties including a wavelength or color that does not fluctuate at all could be useful for many kinds of proposed quant, They need to achieve 100 percent indistinguishability in the photons produced   

    From MIT News: “Quantum dots can spit out clone-like photons” 

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    MIT Widget

    From MIT News

    February 21, 2019
    David L. Chandler

    1
    Scanning Transmission Electron Microscope image (STEM) of single perovskite quantum dots. New study shows that single perovskite quantum dots could be a fundamental building block for quantum-photonic technologies for computing or communications. Image courtesy of the authors.

    System that generates coherent single particles of light could help pave the way for quantum information processors or communications.

    In the global quest to develop practical computing and communications devices based on the principles of quantum physics, one potentially useful component has proved elusive: a source of individual particles of light with perfectly constant, predictable, and steady characteristics. Now, researchers at MIT and in Switzerland say they have made major steps toward such a single photon source.

    The study, which involves using a family of materials known as perovskites to make light-emitting particles called quantum dots, appears today in the journal Science. The paper is by MIT graduate student in chemistry Hendrik Utzat, professor of chemistry Moungi Bawendi, and nine others at MIT and at ETH Zürich, Switzerland.

    The ability to produce individual photons with precisely known and persistent properties, including a wavelength, or color, that does not fluctuate at all, could be useful for many kinds of proposed quantum devices. Because each photon would be indistinguishable from the others in terms of its quantum-mechanical properties, it could be possible, for example, to delay one of them and then get the pair to interact with each other, in a phenomenon called interference.

    “This quantum interference between different indistinguishable single photons is the basis of many optical quantum information technologies using single photons as information carriers,” Utzat explains. “But it only works if the photons are coherent, meaning they preserve their quantum states for a sufficiently long time.”

    Many researchers have tried to produce sources that could emit such coherent single photons, but all have had limitations. Random fluctuations in the materials surrounding these emitters tend to change the properties of the photons in unpredictable ways, destroying their coherence. Finding emitter materials that maintain coherence and are also bright and stable is “fundamentally challenging,” Utzat says. That’s because not only the surroundings but even the materials themselves “essentially provide a fluctuating bath that randomly interacts with the electronically excited quantum state and washes out the coherence,” he says.

    “Without having a source of coherent single photons, you can’t use any of these quantum effects that are the foundation of optical quantum information manipulation,” says Bawendi, who is the Lester Wolfe Professor of Chemistry. Another important quantum effect that can be harnessed by having coherent photons, he says, is entanglement, in which two photons essentially behave as if they were one, sharing all their properties.

    Previous chemically-made colloidal quantum dot materials had impractically short coherence times, but this team found that making the quantum dots from perovskites, a family of materials defined by their crystal structure, produced coherence levels that were more than a thousand times better than previous versions. The coherence properties of these colloidal perovskite quantum dots are now approaching the levels of established emitters, such as atom-like defects in diamond or quantum dots grown by physicists using gas-phase beam epitaxy.

    One of the big advantages of perovskites, they found, was that they emit photons very quickly after being stimulated by a laser beam. This high speed could be a crucial characteristic for potential quantum computing applications. They also have very little interaction with their surroundings, greatly improving their coherence properties and stability.

    Such coherent photons could also be used for quantum-encrypted communications applications, Bawendi says. A particular kind of entanglement, called polarization entanglement, can be the basis for secure quantum communications that defies attempts at interception.

    Now that the team has found these promising properties, the next step is to work on optimizing and improving their performance in order to make them scalable and practical. For one thing, they need to achieve 100 percent indistinguishability in the photons produced. So far, they have reached 20 percent, “which is already very remarkable,” Utzat says, already comparable to the coherences reached by other materials, such as atom-like fluorescent defects in diamond, that are already established systems and have been worked on much longer.

    “Perovskite quantum dots still have a long way to go until they become applicable in real applications,” he says, “but this is a new materials system available for quantum photonics that can now be optimized and potentially integrated with devices.”

    It’s a new phenomenon and will require much work to develop to a practical level, the researchers say. “Our study is very fundamental,” Bawendi notes. “However, it’s a big step toward developing a new material platform that is promising.”

    The work was supported by the U.S. Department of Energy, the National Science Foundation, and the Swiss Federal Commission for Technology and Innovation.

    See the full article here .


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    Please help promote STEM in your local schools.


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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 12:01 pm on February 23, 2019 Permalink | Reply
    Tags: "Physicists calculate proton’s pressure distribution for first time", , MIT, ,   

    From MIT News: “Physicists calculate proton’s pressure distribution for first time” 

    MIT News
    MIT Widget

    From MIT News

    February 22, 2019
    Jennifer Chu

    1
    MIT physicists have calculated the pressure distribution inside a proton for the first time. They found the proton’s high-pressure core pushes out, while the surrounding region pushes inward. Credit: Courtesy of the researchers

    The particle’s core withstands pressures higher than those inside a neutron star, according to a new study.

    Neutron stars are among the densest-known objects in the universe, withstanding pressures so great that one teaspoon of a star’s material would equal about 15 times the weight of the moon. Yet as it turns out, protons — the fundamental particles that make up most of the visible matter in the universe — contain even higher pressures.

    For the first time, MIT physicists have calculated a proton’s pressure distribution, and found that the particle contains a highly pressurized core that, at its most intense point, is generating greater pressures than are found inside a neutron star.

    This core pushes out from the proton’s center, while the surrounding region pushes inward. (Imagine a baseball attempting to expand inside a soccer ball that is collapsing.) The competing pressures act to stabilize the proton’s overall structure.

    The physicists’ results, published today in Physical Review Letters, represent the first time that scientists have calculated a proton’s pressure distribution by taking into account the contributions of both quarks and gluons, the proton’s fundamental, subatomic constituents.

    “Pressure is a fundamental aspect of the proton that we know very little about at the moment,” says lead author Phiala Shanahan, assistant professor of physics at MIT. “Now we’ve found that quarks and gluons in the center of the proton are generating significant outward pressure, and further to the edges, there’s a confining pressure. With this result, we’re driving toward a complete picture of the proton’s structure.”

    Shanahan carried out the study with co-author William Detmold, associate professor of physics at MIT. Both are researchers in the Laboratory for Nuclear Science.

    Remarkable quarks

    In May 2018, physicists at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility announced that they had measured the proton’s pressure distribution for the first time, using a beam of electrons that they fired at a target made of hydrogen.


    JLab campus

    The electrons interacted with quarks inside the protons in the target. The physicists then determined the pressure distribution throughout the proton, based on the way in which the electrons scattered from the target. Their results showed a high-pressure center in the proton that at its point of highest pressure measured about 1035 pascals, or 10 times the pressure inside a neutron star.

    However, Shanahan says their picture of the proton’s pressure was incomplete.

    “They found a pretty remarkable result,” Shanahan says. “But that result was subject to a number of important assumtions that were necessary because of our incomplete understanding.”

    Specifically, the researchers based their pressure estimates on the interactions of a proton’s quarks, but not its gluons. Protons consist of both quarks and gluons, which continuously interact in a dynamic and fluctuating way inside the proton. The Jefferson Lab team was only able to determine the contributions of quarks with its detector, which Shanahan says leaves out a large part of a proton’s pressure contribution.

    “Over the last 60 years, we’ve built up quite a good understanding of the role of quarks in the structure of the proton,” she says. “But gluon structure is far, far harder to understand since it is notoriously difficult to measure or calculate.”

    A gluon shift

    Instead of measuring a proton’s pressure using particle accelerators, Shanahan and Detmold looked to include gluons’ role by using supercomputers to calculate the interactions between quarks and gluons that contribute to a proton’s pressure.

    “Inside a proton, there’s a bubbling quantum vacuum of pairs of quarks and antiquarks, as well as gluons, appearing and disappearing,” Shanahan says. “Our calculations include all of these dynamical fluctuations.”

    To do this, the team employed a technique in physics known as lattice QCD, for quantum chromodynamics, which is a set of equations that describes the strong force, one of the three fundamental forces of the Standard Model of particle physics. (The other two are the weak and electromagnetic force.) The strong force is what binds quarks and gluons to ultimately make a proton.

    Lattice QCD calculations use a four-dimensional grid, or lattice, of points to represent the three dimensions of space and one of time. The researchers calculated the pressure inside the proton using the equations of Quantum Chromodynamics defined on the lattice.

    “It’s hugely computationally demanding, so we use the most powerful supercomputers in the world to do these calculations,” Shanahan explains.

    The team spent about 18 months running various configurations of quarks and gluons through several different supercomputers, then determined the average pressure at each point from the center of the proton, out to its edge.

    Compared with the Jefferson Lab results, Shanahan and Detmold found that, by including the contribution of gluons, the distribution of pressure in the proton shifted significantly.

    “We’ve looked at the gluon contribution to the pressure distribution for the first time, and we can really see that relative to the previous results the peak has become stronger, and the pressure distribution extends further from the center of the proton,” Shanahan says.

    In other words, it appears that the highest pressure in the proton is around 1035 pascals, or 10 times that of a neutron star, similar to what researchers at Jefferson Lab reported. The surrounding low-pressure region extends farther than previously estimated.

    Confirming these new calculations will require much more powerful detectors, such as the Electron-Ion Collider, a proposed particle accelerator that physicists aim to use to probe the inner structures of protons and neutrons, in more detail than ever before, including gluons.

    “We’re in the early days of understanding quantitatively the role of gluons in a proton,” Shanahan says. “By combining the experimentally measured quark contribution, with our new calculation of the gluon piece, we have the first complete picture of the proton’s pressure, which is a prediction that can be tested at the new collider in the next 10 years.”

    This research was supported, in part, by the National Science Foundation and the U.S. Department of Energy.

    See the full article here .


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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 3:13 pm on February 20, 2019 Permalink | Reply
    Tags: , , , MIT, , , Study of quark speeds finds a solution for a 35-year physics mystery, The EMC effect: In the nucleus of an iron atom containing many protons and neutrons quarks move significantly more slowly than quarks in deuterium which contains a single proton and neutron, The larger an atom’s nucleus the slower the quarks that move within   

    From MIT News: “Study of quark speeds finds a solution for a 35-year physics mystery” 

    MIT News
    MIT Widget

    From MIT News

    February 20, 2019
    Jennifer Chu

    1
    MIT physicists find quarks move slower in atoms with more pairs of protons and neutrons. Courtesy of the researchers.

    Number of proton-neutron pairs determine how fast the particles move, results suggest.

    MIT physicists now have an answer to a question in nuclear physics that has puzzled scientists for three decades: Why do quarks move more slowly inside larger atoms?

    Quarks, along with gluons, are the fundamental building blocks of the universe. These subatomic particles — the smallest particles we know of — are far smaller, and operate at much higher energy levels, than the protons and neutrons in which they are found. Physicists have therefore assumed that a quark should be blithely indifferent to the characteristics of the protons and neutrons, and the overall atom, in which it resides.

    But in 1983, physicists at CERN, as part of the European Muon Collaboration (EMC), observed for the first time what would become known as the EMC effect: In the nucleus of an iron atom containing many protons and neutrons, quarks move significantly more slowly than quarks in deuterium, which contains a single proton and neutron. Since then, physicists have found more evidence that the larger an atom’s nucleus, the slower the quarks that move within.

    “People have been wracking their brains for 35 years, trying to explain why this effect happens,” says Or Hen, assistant professor of physics at MIT.

    Now Hen, Barak Schmookler, and Axel Schmidt, a graduate student and postdoc in MIT’s Laboratory for Nuclear Science, have led an international team of physicists in identifying an explanation for the EMC effect. They have found that a quark’s speed depends on the number of protons and neutrons forming short-ranged correlated pairs in an atom’s nucleus. The more such pairs there are in a nucleus, the more slowly the quarks move within the atom’s protons and neutrons.

    Schmidt says an atom’s protons and neutrons can pair up constantly, but only momentarily, before splitting apart and going their separate ways. During this brief, high-energy interaction, he believes that quarks in their respective particles may have a “larger space to play.”

    “In quantum mechanics, anytime you increase the volume over which an object is confined, it slows down,” Schmidt says. “If you tighten up the space, it speeds up. That’s a known fact.”

    As atoms with larger nuclei intrinsically have more protons and neutrons, they also are more likely to have a higher number of proton-neutron pairs, also known as “short-range correlated” or SRC pairs. Therefore, the team concludes that the larger the atom, the more pairs it is likely to contain, resulting in slower-moving quarks in that particular atom.

    Schmookler, Schmidt, and Hen as members of the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility, have published their results today in the journal Nature.

    From a suggestion to a full picture

    In 2011, Hen and collaborators, who has focused much of their research on SRC pairs, wondered whether this ephemeral coupling had anything to do with the EMC effect and the speed of quarks in atomic nuclei.

    They gathered data from various particle accelerator experiments, some of which measured the behavior of quarks in certain atomic nuclei, while others detected SRC pairs in other nuclei. When they plotted the data on a graph a clear trend appeared: The larger an atom’s nucleus, the more SRC pairs there were, and the slower the quarks that were measured. The largest nucleus in the data — gold — contained quarks that moved 20 percent more slowly than those in the smallest measured nucleus, helium.

    “This was the first time this connection was concretely suggested,” Hen says. “But we had to do a more detailed study to build a whole physical picture.”

    So he and his colleagues analyzed data from an experiment that compared atoms of different sizes and allowed measuring both the quarks’ speed and the number of SRC pairs in each atom’s nucleus. The experiment was carried out at the CEBAF Large Acceptance Spectrometer, or CLAS detector, an enormous, four-story spherical particle accelerator at the Thomas Jefferson National Laboratory in Newport News, Virginia.

    Jlab CEBAF

    Within the detector, Hen describes the team’s target setup as a “kind of a Frankenstein-ish thing,” with mechanical arms, each holding a thin foil made from a different material, such as carbon, aluminum, iron, and lead, each made from atoms containing 12, 27, 67, and 208 protons and neutrons, respectively. An adjacent vessel held liquid deuterium, with atoms containing the lowest number of protons and neutrons of the group.

    When they wanted to study a particular foil, they sent a command to the relevant arm to lower the foil of interest, following the deuterium cell and directly in the path of the detector’s electron beam. This beam shot electrons at the deuterium cell and solid foil, at the rate of several billion electrons per second. While a vast majority of electrons miss the targets, some do hit either the protons or neutrons inside the nucleus, or the much tinier quarks themselves. When they hit, the electrons scatter widely, and the angles and energies at which they scatter vary depending on what they hit — information that the detector captures.

    Electron tuning

    The experiment ran for several months and in the end amassed billions of interactions between electrons and quarks. The researchers calculated the speed of the quark in each interaction, based on the electron’s energy after it scattered, then compared the average quark speed between the various atoms.

    By looking at much smaller scaterring angles, corresponding to momentum transfers of a different wave length, the team were able to “zoom out” so that electrons would scatter off the larger protons and neutrons, rather than quarks. SRC pairs are typically extremely energetic and would therefore scatter electrons at higher energies than unpaired protons and neutrons, which is a distinction the researchers used to detect SRC pairs in each material they studied.

    “We see that these high-momentum pairs are the reason for these slow-moving quarks,” Hen says.

    In particular, they found that the quarks in foils with larger atomic nuclei (and more proton-neutron pairs) moved at most 20 percent slower than deuterium, the material with the least number of pairs.

    “These pairs of protons and neutrons have this crazy high-energy interaction, very quickly, and then dissipate,” Schmidt says. “In that time, the interaction is much stronger than normal and the nucleons have significant spatial overlap. So we think quarks in this state slow down a lot.”

    Their data show for the first time that how much a quark’s speed is slowed depends on the number of SRC pairs in an atomic nucleus. Quarks in lead, for instance, were far slower than those in aluminum, which themselves were slower than iron, and so on.

    The team is now designing an experiment in which they hope to detect the speed of quarks, specifically in SRC pairs.

    “We want to isolate and measure correlated pairs, and we expect that will yield this same universal function, in that the way quarks change their velocity inside pairs is the same in carbon and lead, and should be universal across nuclei,” Schmidt says.

    Ultimately, the team’s new explanation can help to illuminate subtle yet important differences in the behavior of quarks, the most basic building blocks of the visible world. Scientists have an incomplete understanding of how these tiny particles come to build the protons and neutrons that then come together to form the individual atoms that make up all the material we see in the universe.

    “Understanding how quarks interact is really the essence of understanding the visible matter in the universe,” Hen says. “This EMC effect, even though 10 to 20 percent, is something so fundamental that we want to understand it.”

    This research was funded, in part, by the U.S. Department of Energy, and the National Science Foundation.

    See the full article here .


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    Please help promote STEM in your local schools.


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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 12:02 pm on February 20, 2019 Permalink | Reply
    Tags: "Robots track moving objects with unprecedented precision", , MIT, RFID tags,   

    From MIT News: “Robots track moving objects with unprecedented precision” 

    MIT News
    MIT Widget

    From MIT News

    February 18, 2019
    Rob Matheson

    System uses RFID tags to home in on targets; could benefit robotic manufacturing, collaborative drones, and other applications.

    1
    MIT Media Lab researchers are using RFID tags to help robots home in on moving objects with unprecedented speed and accuracy, potentially enabling greater collaboration in robotic packaging and assembly and among swarms of drones. Photo courtesy of the researchers.

    A novel system developed at MIT uses RFID tags to help robots home in on moving objects with unprecedented speed and accuracy. The system could enable greater collaboration and precision by robots working on packaging and assembly, and by swarms of drones carrying out search-and-rescue missions.

    In a paper being presented next week at the USENIX Symposium on Networked Systems Design and Implementation, the researchers show that robots using the system can locate tagged objects within 7.5 milliseconds, on average, and with an error of less than a centimeter.

    In the system, called TurboTrack, an RFID (radio-frequency identification) tag can be applied to any object. A reader sends a wireless signal that reflects off the RFID tag and other nearby objects, and rebounds to the reader. An algorithm sifts through all the reflected signals to find the RFID tag’s response. Final computations then leverage the RFID tag’s movement — even though this usually decreases precision — to improve its localization accuracy.

    The researchers say the system could replace computer vision for some robotic tasks. As with its human counterpart, computer vision is limited by what it can see, and it can fail to notice objects in cluttered environments. Radio frequency signals have no such restrictions: They can identify targets without visualization, within clutter and through walls.

    To validate the system, the researchers attached one RFID tag to a cap and another to a bottle. A robotic arm located the cap and placed it onto the bottle, held by another robotic arm. In another demonstration, the researchers tracked RFID-equipped nanodrones during docking, maneuvering, and flying. In both tasks, the system was as accurate and fast as traditional computer-vision systems, while working in scenarios where computer vision fails, the researchers report.

    “If you use RF signals for tasks typically done using computer vision, not only do you enable robots to do human things, but you can also enable them to do superhuman things,” says Fadel Adib, an assistant professor and principal investigator in the MIT Media Lab, and founding director of the Signal Kinetics Research Group. “And you can do it in a scalable way, because these RFID tags are only 3 cents each.”

    In manufacturing, the system could enable robot arms to be more precise and versatile in, say, picking up, assembling, and packaging items along an assembly line. Another promising application is using handheld “nanodrones” for search and rescue missions. Nanodrones currently use computer vision and methods to stitch together captured images for localization purposes. These drones often get confused in chaotic areas, lose each other behind walls, and can’t uniquely identify each other. This all limits their ability to, say, spread out over an area and collaborate to search for a missing person. Using the researchers’ system, nanodrones in swarms could better locate each other, for greater control and collaboration.

    “You could enable a swarm of nanodrones to form in certain ways, fly into cluttered environments, and even environments hidden from sight, with great precision,” says first author Zhihong Luo, a graduate student in the Signal Kinetics Research Group.

    The other Media Lab co-authors on the paper are visiting student Qiping Zhang, postdoc Yunfei Ma, and Research Assistant Manish Singh.

    Super resolution

    Adib’s group has been working for years on using radio signals for tracking and identification purposes, such as detecting contamination in bottled foods, communicating with devices inside the body, and managing warehouse inventory.

    Similar systems have attempted to use RFID tags for localization tasks. But these come with trade-offs in either accuracy or speed. To be accurate, it may take them several seconds to find a moving object; to increase speed, they lose accuracy.

    The challenge was achieving both speed and accuracy simultaneously. To do so, the researchers drew inspiration from an imaging technique called “super-resolution imaging.” These systems stitch together images from multiple angles to achieve a finer-resolution image.

    “The idea was to apply these super-resolution systems to radio signals,” Adib says. “As something moves, you get more perspectives in tracking it, so you can exploit the movement for accuracy.”

    The system combines a standard RFID reader with a “helper” component that’s used to localize radio frequency signals. The helper shoots out a wideband signal comprising multiple frequencies, building on a modulation scheme used in wireless communication, called orthogonal frequency-division multiplexing.

    The system captures all the signals rebounding off objects in the environment, including the RFID tag. One of those signals carries a signal that’s specific to the specific RFID tag, because RFID signals reflect and absorb an incoming signal in a certain pattern, corresponding to bits of 0s and 1s, that the system can recognize.

    Because these signals travel at the speed of light, the system can compute a “time of flight” — measuring distance by calculating the time it takes a signal to travel between a transmitter and receiver — to gauge the location of the tag, as well as the other objects in the environment. But this provides only a ballpark localization figure, not subcentimter precision.

    Leveraging movement

    To zoom in on the tag’s location, the researchers developed what they call a “space-time super-resolution” algorithm.

    The algorithm combines the location estimations for all rebounding signals, including the RFID signal, which it determined using time of flight. Using some probability calculations, it narrows down that group to a handful of potential locations for the RFID tag.

    As the tag moves, its signal angle slightly alters — a change that also corresponds to a certain location. The algorithm then can use that angle change to track the tag’s distance as it moves. By constantly comparing that changing distance measurement to all other distance measurements from other signals, it can find the tag in a three-dimensional space. This all happens in a fraction of a second.

    “The high-level idea is that, by combining these measurements over time and over space, you get a better reconstruction of the tag’s position,” Adib says.

    The work was sponsored, in part, by the National Science Foundation.

    See the full article here .


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